Thermomagnetic relay



Patented May 22, 1945..

UNITED STATES PATENT OFFICE.

THERMOMAGNETIC RELAY George W. Crise, Columbus, Ohio, assignor to Crise Electric Manufacturing Company, Golumbus, Ohio, a corporation of Ohio Application August 3, 1943, Serial No. 497,173 2 Claims. (!.161-1) The purpose of my invention is to provide an improved relay for eifecting the operationiof electric motors or valves 'used by furnace stokers, oil burners and the like, in accordance with the correlated operation of a thermostat, or other delicate switch, a principal object being to improve present devices for this purpose from a standpoint oi emciency, reliability and structural simplicity.

Another object of the invention is to provide a relay having incorporated in its operation a time delay feature adapted to prevent chattering or dangerous short cycle operation of associated electrical equipment, since undesired short cycle operation tends to burn or fuse the starting windings of a stoker motor, or the coil windings of a solenoid valve, and is often attributable to vibration or improper adjustment or installation of an associated room thermostat.

A further object is to providea relay capable of making and breaking a heavy electric circuit while consuming in its own windings a very small I current.-

An additional object is to provide ciated thermostat is required to interrupt only a small fraction of the current flowing through the relay windings.

For a further understanding of the invention, reference is to be had to the accompanying drawing wherein is illustrated a schematic view=disclosing the relay comprising the' present invention, and associated clock-controlled thermostat and uniting circuits.

Referring more particularly to the drawing, the

numerals l and 2 indica the leads of a commercial power circuit which may be of a standard alternating current type. Connected with these leads are the terminals of a primary transformer coil 3 which, preferably, is applied aroundione of the legs of a substantially rectangular, laminated transformer frame 4. Surrounding n- I relay in i which is incorporated means wherebyhe asso 30 are in relative engagement, current from the 4 31, the latter surrounding but being electrically other leg of the frame 4 is a low-voltage sec-' ondary coil 5 in which current flow is induced from the continuously'energized primary coil 8.

The ends of the coil 5 extend to terminals 6" and I. From the terminal 6 a conductors leads to.

tone of the terminal pos 9 of a clock mechanism II, the latter beingemployed for eflecting day and nightgiontrol over an associated thermostat, indicated nerally by the numeral l I. The other terminal post I! of the clock mechanism is joined with a conductor i! which leads to the terminal I. By this arrangement, a low voltage alternating'current is continuously applied to the clock v The transformer frame is formed to provide spaced poles I4 and It, the space between the poles providing a flux and current limiting gap It. The bottom of the pole I4 is bifurcated to provide spaced legs indicated at ll and I8, and the terminating end-of the pole I5 is notched as at l9. Wrapped around the leg I! is a shading coil 20, one end of thiscoil being connected as at II with a terminal screw 22 mounted in the insulated contact frame ,23, the other end of the shading coil extending to and being joined with the terminal 8.

The thermostat II- has been shown as comprising a rockable stud 24, which carries a crank arm 25. The outer end of this arm is linked as at 28 to the operating arm 21 of the clock mechanism I0, so that the stud 24 may be rocked at different hours of the day by the clock mechanism to control the operation of the thermostat in a wellknown manner.

Connected with the stud 24 is one end ofa spiral bimetallic element 28, the free end of which terminates in a movable contact 29. This contact, through the operation of the element 28, inresponding to different temperatures, is adapted to be brought into and out of engagement with a normally stationary but adjustable contact provided on the ,outer end of a screw II, the latter being supported in a threaded bor provided in an insulating block, shown at 32.

The conductor 8 is electrically joined as at 33 with the stud 24, and when the contacts 28 and secondary winding of the transformer flows through'the element 2!, the contacts 29 and 30 and the screw ii to a'ten'ninal post 34, mounted in the block 32 and disposed in electrical engagement with the screw 3i. From the post 34, a con- (motor 35 extends to a terminal'post 38. To this post there is connected one end of a resistor coil spaced from a-bimetallic warping bar 38, said bar having its high expanding side arranged at the bottonithereoi.

One end of the Warning bar is "secured to a block 39 of insulatingmaterial, while the outer or free end oi the bar carries an armature ill. Normally, this armature is disposed in engagement with a permanent magnet indicated at 4|, the

latter being, in mounted on an insulated support shown at, the armature being spaced from the pole extremities of the transformer irame. Also, mechanically carried bythe outer end of the warping bar'but electrically spaced therefrom is a bowedsprins ll which carries at its free end a contact 44 and is joined with resistor coil 31. With the warping bar positioned as shown in the drawing, the contact 44 engages with a stationary but adjustable contact 45 formed in the upper end of a screw 46 which is threaded in the support 42. Contacting the screw 46 isa terminal member 41 from which extends a conductor 48,1eading to the terminal l of the secondary winding of the transformer.

It will be seen that when the temperature surrounding the thermostat ll falls to a predetermined extent, the bimetallic element 28 of said thermostat will flex to bring the contacts 29 and 30 together, When this engagement occurs, current flows from the secondary winding of the transformer through the thermostat-to the conductor 35, and thence through the resistor coil 31 of the warping bar, passing through contacts 44 and 45 and returning to the secondary winding of the transformer through the conductor 48. The flow of current through the resistor coil causes the latter to release heat which, in turn, produces fiexure of the warping bar 38. After a certain period of time, this flexure forms sumcient energy to overcome the attraction exercised by the permanent magnet M on the armature Ml, so that the latter is brought into engagement, by a quick motion, with the terminal pole I4 of the transformer. When this occurs, a bowed spring 49 carrying at its free end a contact 50, and which spring is mounted on the armature 40, is

brought into contact with one end of a stationary but adjustable screw 5! threaded in the contact frame 23, so that current may flow through the shading coil 20.

Carried by the frame 23 is a second contact screw 52 normally spaced from a contact 53 carried by an insulating strip 54. This strip is supported by the outer end of a leaf spring 55, the inner or fixed end of said spring being secured to the lower leg of the frame 23. The tendency of the spring 55 is to maintain the contact 53 in engagement with the contact 52. However, when the armature is attracted by the magnet 41, one end of the armature bears on the strip 54, holding the contacts 52 and 53 out of engagement with each other. When the armature is attracted by the pole extremities l1 and 18 of the transformer, the upward movement of the armature releases the strip 54, allowing the latter to respond sharply to the action of the spring 55 so that the contacts 52 and 53 are quickly engaged. 4 The screw 52 is electrically connected with a terminal 58, and likewise the spring 55 is electrically connected with a terminal 51. These terminals are disposed in a circuit 58 in which is arranged 'an electric motor 59 used as the operating unit of a furnace stoker. In the event the heater is of the ty e consuming a gaseous or liquid fuel, the energizing coil of a solenoid operated valve may be substituted for the motor 59.

Operation cidental short-circuiti'ng or over-voltage. Upon closure of the thermostat contacts 29 and 30, by

tacts 44 and 45.

as rates a drop or room temperature, the circuit is completed through the heater coil 31, causing the bimetallic warping bar 38 to be gradually heated. In approximately one minutes time, more or less. suflicient tension will be established in the bimetallic bar to cause the armature 40 to separate from the magnet 41, moving the armature by quick action against the pole terminals l4 and 15 of the transformer core. Concurrently with this action, current flow through the resistor coil 37 is interrupted by the separation of the con- However, the contacts 50 and Si are brought into engagement, thus energizing the shading coil 20 through the room thermostat.

As the warping bar 38 cools off, over a period of 1 to 2 minutes, the armature would normally be drawn down into engagement with the magnet 4! were it not for the action 01' the shading coil 20. This coil increases the normal holding action of the transformer poles I4 and E5 on the armature to an extent about 8 to 10 times that necessary to hold the armature, this condition obtaining just as long as the shading coil circuit is complete through the room thermostat.

While the armature 40 is raised and held by the transformer poles, the insulating strip 54 is released, thereby allowing the spring 55 to close the contacts 52 and 53, completing the control circuit which governs the operation of associated electrically actuated fuel-supplying means for furnaces or other heaters.

When sufiicient heat has been generated by the action of the furnace or heater to satisfy the room thermostat, the contacts 29 and 30 will separate, breaking the circuit through the shading coil 20. This results inreleasing the armature 40, which falls under the pull of gravity, the spring tension of the unheated warping bar and the action of the magnet 4| causing quick movement of the armature so that the same strikes the strip 54 and separates the contacts 52 and 53, thereby interrupting the circuit 58 and discontinuing active operation of the heating means. At the same time, it will be observed that the contacts 50 and 5| are separated and the heater circuit through contacts 44 and 45 reestablished except for the closing of the thermostat contacts, thus completing one complete cycle of operation.

It will also be noted that when the armature 40 is in contact With the pole pieces of the transformer, it partially shunts the magnetic gap 18, which offsets the magnets flux consumed by the shading coil 20, thus maintaining substantially constant voltage in the secondary winding of the transformer, supplying a low voltage current for the electric clock mechanism.

The thermostat I I is required merely to handle a small part of the current flowing through the relay, since the thermostat is connected either in the warpi g bar heating circuit or the shading coil circui ,and not in the primary or directly across the secondary as is common in the art. Since a period of time of approximately one minute is consumed to heat the warping bar 38, a thermostat current or less than one watt is sufficient to handle a heavy switching load.

It is important that the heated warping bar shall hold the armature 40 firmly against the pole pieces It and I5 until the bar cools suinciently irrespective of the action of the shading coil 20. This prevents the relay from stopping the Stoker or fuelburner of an associated heater until it has operated approximately one minute, even though the thermostat for some cause should break connections momentarily; for instance, as

warp her preventing a restarting of the heater fora like period after being stopped. Once the warping bar has cooled, however,-the room thermostat can stop the stoker or oil burner instantly upon separation of its contacts 29 and-8d.

It is also important to note that since only approximately one-eighth to one-tenth of the energy'is required to hold the armature t8 against the transformer poles as would be required to lift the armature magnetically, the relay saves more than enough current by this method of operation to supply current for an electric clock, which would otherwise require a separate transformer to supply low voltage in accordance with wiring codes, a simplified installation of the complete equipment thus resulting.

I claim: i

1. Thermally responsive switch mechanism comprising a transformer having" a frame formed with spaced poles, a primary coil surrounding said frame connected with a source of electrical emote I nesult oi vibration, the slow heating of the energy, a low voltage secondary coil surrounding said frame, a thermostat including an electrically actuated clock mechanism, a circuit for said clock mechanism joined with said secondary coil,

bimetallic element having one end secured to d turnable member, a. movable contact carried by the free end of said bimetallic element, a stationary but adjustable contact adapted for engagement and disengagement with said movable contact upon. flexure of said. element in response to temperature changes, a circuit leading from ing through said thermostat} a permanent magnet disposed adjacent to said armature a shadin: coil surrounding one or the poles .01 said transformer frame, a circuit for said shading coil to temperature changes, a circuit leading from :a turnable member adapted to be rocked at predetermined intervals by said clock mechanism, a

forming another trench oi cold thermostat circult, and circuit melting and breaking devices for said resistor and shading coil circuits actuated icy the movemenm of said armature in response to thermal chances in said warping bar and attract-ion exerted on said armoture by sold permoment magnet and transformer poles.

2. Thermally responsive switch mechanism comprising a transformer having a frame iormed 'tumuble member, a movable contact carried by the free end or sold bimeic element, c. stationary hut adjustable contact adapted'ior eneasement and disengagement with said movable contact upon denture of said element in response the secondary coil of said transformer to said movable and stationary contacts, a bimetallic warp bar, it support to which one end of sold bar is secured, on armature carried by the outer movable end of said bar, a, heating resistor dimpcsed odiacent to said warping bar, a circuit for said resistor forming a branch of the circuit passing through said thermostat, a permanent mognet disposed adjacent to said armature, a shading coil surrounding one oi the poles of said transformer frame, a circuit for said shading coil iorm= ing another branch of said thermostat circuit, circuit making and breaking devices for said resistor and shading coil circuits actuated by the movements of said armature in response to thermal changes in said warping bar and the at-= traction exerted on said armature by said pee nent magnet and transformer poles, a power sir-- i cult, and circuit making and breaking devices for said power circuit actuated by the movements oi said armature.

- ononon w. omen. 

